The use of combinations of copolymers containing succinic anhydride and polyhydroxyl compounds as binders for lacquers and coating compositions is already known from European Published Application No. 48 128. However, the principle of this prior publication cannot be applied to the reaction of amines with anhydrides because this reaction takes place very quickly, even at room temperature, leading to crosslinked products through cleavage of the anhydride. The resulting, extremely short standing times have hitherto prevented polyanhydrides and polyamines from being used together in coating systems.
One possibility of increasing the standing times is to use oxazolanes instead of the amines.
Water-hardening compositions of oxazolanes and polyanhydrides are known in the principle from German Offenlegungeschrift No. 2 610 406 where oxazolanes are combined with polyanhydrides for water-hardening sealing compounds and adhesives. Reaction products of polyunsaturated fatty acids with maleic anhydride and polyanhydrides of C.sub.3 -C.sub.6 alkyl (meth)acrylate and maleic anhydride, more especially of butyl acrylate and maleic anhydride, are described as suitable polyanhydrides.
Tests Conducted by the present inventors have been shown that the systems specifically described by German No. 2 610 406 are still greatly in need of improvement in regard to their suitability for the production of high-quality colorless lacquer films combining extreme hardness with high resistance to solvents and chemicals. This applies both to the systems based on copolymers of maleic anhydride and butyl acrylate which are described in the Examples and to the systems based on reaction products of maleic anhydride with polyunsaturated fatty acid esters which lead to yellowing end products.
Accordingly, the object of the present invention is to provide new binder compositions based on copolymers of maleic anhydride with other olefinically unsaturated monomers and oxazolanes which satisfy exacting practical requirements in regard to their technical lacquer properties, particularly their hardness and resistance to solvents and chemicals, and in regard to the yellowing resistance of the coatings produced from them.